Lead is an odorless, silver-bluish-white metal that is insoluble in water and has no known biological function in humans [1]. Exposure to lead and lead compounds can be harmful to humans, especially children [1-15]. Needleman notes that the poisonous properties of lead were first known to be described in the second century B.C. by the Greek physician, Nikander [2]. Nikander took note that after ingestion of lead by a person, colic and paralysis usually followed [2]. In spite of its poisonous properties, according to the U.S. Department of Health and Human Services, lead still managed to become the fifth most used metal in the world, behind iron, copper aluminum and zinc [3]. Due to its toxicity and prevalence in society, it is important that there is a proper determination of recent lead uptake in a particular area [1-5,7,9,14-22]. Determining the concentration of lead in blood is seen as a way of doing this [4,5,14-22]. Therefore, there is a need for reliable analytical techniques that can properly determine the concentration of lead in a blood.
Lead in our environment:
According to the a 2002 U.S. Environmental Protection Agency (EPA) report, Lead (Pb) is one of the six principle air pollutants (criteria pollutants) in our environment and one of four pollutants that are emitted directly from different sources [3,6]. Lead and lead compounds are commonly used in a variety of products, including piping, petrol additives, weights, professional paints, dyes, ceramics, ammunition, homeopathic remedies, cosmetics, cable coverings, sheet metal [1-3,6]. In the U.S. organic leads (mainly tetraethyl lead and tetramethyl lead) were once used as anti-knocking agents in motor vehicle fuels (primarily gasoline) [3]. As a result, automotive sources were the major contributor of lead emissions to the atmosphere, particularly in North America. In the early 1970’s the EPA initiated a phase-out of lead in gasoline [3,6]. Around this time, other countries also implemented programs aimed at decreasing the amount of lead emitted into the environment [1-3,6]. Since then, in the U.S., the use of lead in gasoline has fallen to 1% of its 1970 level and in 1996 the use of lead in fuel for on-road vehicles was completely banned [3,6]. By 2002 the overall emissions of lead had decreased about 93% [6]. As a result of similar regulations as in the U.S., between the years 1984-95, population blood lead concentration saw a “three-fold” decrease in the United Kingdom [7]. Today, lead’s largest use is in lead-acid storage batteries for motor vehicles and industrial use [3,6]. Also, the major sources of lead emissions to the atmosphere are now industrial processes, mainly the processing of metals [1-3,6].
Figure 1:
Lead Emissions in the U.S. from 1982-2002 [6]
As a result of lead and lead compound’s use in industrial settings prior to 3 decades ago, adults were the main concern when lead exposure, particularly occupational exposure, was disused [1-3]. As the toxic affects lead has on humans were discovered regulations were put in place that decreased the number of adult lead poisoning cases reported each year [1-3,6-7]. The focus was then shifted from adults exposed to high does in industrial environments toward children, who may not present symptoms of lead poisoning until long after exposure [1-3,7,10,14]. Children are now at a greater risk of acute lead poisoning and plumbism (chronic lead poisoning) than adults [1-3,5,7,9,10,14,15]. In 1988 it was estimated that about 4 million children in North America had blood lead concentrations about 0.72 μmol/L (7.2x10-7 M), and thus were considered to be at risk of developing lead poisoning [7]. A lot of houses constructed before 1950 contain lead based paint [1]. Particularly in North America these houses may still be a health risk [1]. Today, Lead-based paint, lead dust, and lead in the soil are the leading causes of lead poisoning, particularly plumbism in children [1-3,7,9,14].
Lead entering the human body:
Lead can be released into the environments from both natural and anthropogenic sources [1-3,6,9]. The majority of our exposure and thus lead that are absorbed into the body results from anthropogenic sources [1-3,6,9]. When released, lead exists in both inorganic and organic forms, with inorganic being the more toxic to humans [3,7]. Despite its form, after emission into the environment lead is not degraded and is always available for human exposure [3,7].
Lead has a number of routes it can take to enter the human body [1-3,5-7,8,9,11,14] . It can be absorbed through the gastrointestinal tract (ingested), through the respiratory system (inhaled), or in rare occasions through dermal contact (contact with the skin) [1-3,5-7,8,9,11,14]. In adults, the respiratory tract is the main route of absorption, with anywhere from 30-70% of inhaled lead finding its way in the blood circulation [1-3,5-7,8,9,11,14]. This is because lead fumes are mainly found in industry [3,5,6]. Absorption that occurs through the gastrointestinal tract in adults is often incomplete, with only about 8-15% of ingested lead finding its way into blood circulation [1-3,5-7,8,9,11,14]. In children, the gastrointestinal tract is the primary sources of absorption, with about 50% of ingested lead ending up in blood circulation [1-3,5-7,8,9,10,11,14]. This is because of the fact that most children who develop lead poisoning, particularly in North America, do so from ingestion of lead paint chips [1-3,5-7,8,9,11,14]. When it comes to inhalation of lead and lead compounds the percent of lead that ends up in blood stream of children is comparable to that of adults, but children inhale a larger volume of air relative to their body sizes [7]. As a direct result of children’s large inhaled air to body size ratio, children absorb around three times more lead from the environment that adults [7]. In both adults and children, dermal absorption of lead and lead compounds is so rare and minute that the amount of lead that makes its way into the blood stream through dermal contact is negligible [2,3,7,11].
When lead or lead compounds are inhaled, particle size is the most important determinant of absorption [7]. Having an Iron deficiency and low calcium levels can increase absorption of lead by ingestion [2,7]. When in the body, lead tends to be stored in three major pools [2,7]. The greatest storage pool for lead is in dentine and the skeleton, which accounts for about 95% of lead decomposition in the body [2,7]. The next largest pool is comprised of the skin and muscle, which accounts for about 3% of lead deposition in the body [2,7]. The smallest and most important pool is the blood pool [2,7]. The blood pool of lead is “rapidly exchangeable” and despite its importance, accounts for only about 2% (95% is bound to erythrocyte membrane and 5% is in plasma) of the lead deposition in the body [2,7]. The lead in blood is the most important pool because the concentration of lead in blood can be used as an index of lead exposure [1-4,7,9,10,14,15]. Gordon describes blood lead as having a half-life of about 35 days, and bone lead as having a half-life of about 20-30 years [2,7].
Children, particularly infants, are at an even greater risk of lead poisoning due to their high rate of hand to mouth contact [10].
Lead’s effect on the human body:
General affects:
Lead poisoning is often asymptomatic, particularly acute poisoning and poisoning from lead with mild toxicity [1-3,5-7,8,9,11,14]. Some general symptoms of acute poisoning include: metallic taste, abdominal discomfort, lethargy, anorexia, headaches, and muscle weakness [1-3,5-7,8,9,11,12,14]. Some general symptoms of chronic lead poisoning (plumbism) include: vomiting, abdominal pain, coma, and a bluish lead line on the gums [1-3,5-7,8,9,11,12,14] .
Figure 2:
Lead's Effect on Teeth [11]
Biochemical and Blood affects:
Lead has a number of biochemical properties that account for its toxicity in humans [2,7]. Of these properties is that lead is a divalent cation that has the ability to bind strongly to sulfhydryl groups on proteins [2,7]. Lead, therefore, inhibits sulfhydryl dependent enzymes by distorting their structure [2,7]. The more important of the enzymes that lead inhibits include: 5-Aminolaevulinic acid dehydratase (ALAD), coproporphyrinogen oxidase, and ferrochelatase [2,7]. All of which are important in the synthesis of haem (heme[2,7,13]).
Figure 3:
Haem (heme) synthesis in the body [7]
Heme (haem) is an iron-containing non protein part of a hemoglobin molecule that allows for red blood cells to carry oxygen throughout the body [2,7,13]. Heme groups in hemoglobin molecules are comprised of a cyclic structure of four pyrrole compounds with an atom of iron at the center [2,7,13]. By interrupting the synthesis of heme in the body, lead increases the amount of unhealthy lead blood cells in circulation [2,7,13]. This effect of lead on the body is the reason that chronic exposure to lead can lead to development of anemia, which typically occurs when lead blood concentrations become greater than 2.4 μmol/L (2.4x10-6 M) [1,2,5-7,8,9,11,12,13,14]. Another biochemical property of the divalent lead cation is its ability to mimic calcium in the body [2,7]. This allows lead to compete for binding sites with calcium, which adversely affects endocrine and neuronal function [2,7]. Lead is picked up by mitochondria in cells distorting their shape, and inhibiting the proper execution of oxidative phosphorylation (cellular respiration) [1,2,7,8,9,11,12,14]. The last toxic biochemical property of lead is its ability to interact with nucleic acid binding proteins. This affects gene transcription of DNA, and as a result gene regulation [2,7].
Neurological and developmental affects:
Lead adversely affects the central nervous system (CNS) in adults, but does so to a greater extent in children [1,2,7-9,11,12,14]. Lead poisoning symptoms are primarily lethargy, fatigue and motor neuropathy, and encephalopathy (commonly seen in children with chronic lead exposure) [1-3,7-9,11,12,14]. Lead’s ability to mimic calcium allows it to interfere in certain neurotransmission pathways [2,7,10]. It causes sporadic neurotransmitter release and inhibits the needed stimulated releases [2,7,10]. Prenatal exposure to lead can stunt fetal development and have an adverse effect on the CNS and thus brain development of the resulting child [1-3,7-9,11,12,14,15]. Lead exposure is particularly dangerous for children younger than 6 years old [1-3,7-9,11,12,14]. Before this age, even the minutest exposure to lead can greatly damage the still developing central nervous system [2,3,7,9,10,15]. A study published in Environmental Health Perspectives illustrates that children under the age of 6 with blood lead concentrations as low as 5μg/dL have lower intelligence quotients (IQs) that they would have if they were not exposed to lead [2,7,9,10,14]. Over the age of six, lead exposure and, more specifically, blood lead concentrations in children have proven to be inversely proportional to full scale IQ and performance IQ scores[2,7,9,10,14].
Renal affects:
Lead neprophaty, interstitial nephritis, and renal failure are typically associated with chronic high levels of lead exposure and are seen mainly in industrial workers [1-3,7,8,9,11,12,14]. Acute lead poisoning typically presents itself as glycosuria, hyperphosphaturia, and aminoaciduria [1-3,7,8,9,11,12,14].
Diagnosing lead poisoning:
Diagnosis of acute lead poisoning and plumbism is difficult, mainly because most people exposed to lead are asymptomatic [1-3,7,8,9,11,12,14]. Also, the symptoms that do arise are common enough to be dismissed as individual conditions [1-3,7,8,9,11,12,14]. A physician’s discretion must be used, with the risk of a patient’s exposure to lead being a critical identifier for possible lead poisoning [1-3,7,8,9,11,12,14]. After risk is established, analytical techniques must be used to determine the exact concentration of lead in blood, which is the primary indicator of exposure [1-4,7,9,10,14-22]. Plasma lead levels have proven to be a greater indicator of exposure and risk than whole blood lead levels, when analyzing a sample of blood [5,16,17,20]. In some more modern techniques urine can be used to establish proof of exposure [1,2,3,7,22]. Techniques involving urine, however, can be unreliable and are primarily used in undeveloped nations [1]. In these nations lead concentrations are typically greater, thus requiring less sensitive analytical techniques [1,22].
Analyzing lead in the blood:
Inductively Coupled Plasma Mass Spectrometry:
Use:
Inductively coupled plasma mass spectrometry (ICP-MS) is a relatively modern technique used to analyze lead in blood plasma, rather than the lead in whole blood [4,5,16]. ICP-MS is widely used in the analysis of dried blood spots taken from newborns and infants to examine prenatal and neonatal lead exposure [10,15,16]. By taking the lead isotope ratio of environmental samples and comparing them with blood samples lead exposure levels for a particular area can be established [16]. Inductively coupled plasma (ICP) is known to be a superior ion source, allowing for efficient ionization, even in the mists of multiple ion sources, and for isotope ratio measurements with external standardization for an instrumental mass discrimination correction during ICP-MS [16].
Deduction:
When analyzed using ICP-MS the concentrations of matric elements prove to be inversely proportional to the precision of the determined lead isotope ratios [16]. This is one factor that contributes to a decreased signal intensity, which is a problem commonly experienced when performing ICP-MS [16]. This lowed signal intensity could also be attributed to ionization interference or space-charge effect [16].
ICP-MS is useful and accurate when determining isotope ratio measurements of lead in standard solution [16,17]. At concentrations greater than about 10mgkg-1, however, matrixes have proven to lower this accuracy in solution samples [16]. Despite this effect matrices have on the results of ICP-MS, it is still in general one of the more reliable analytical techniques that can be used when determining blood lead levels, and as a result, potential exposure or risk of exposure in a particular environment [4,7,15,16-22].
Inductively Coupled Plasma Mass Spectrometry + Size Exclusion Chromatography:
Combining size exclusion chromatography (SEC) to the previously described ICPMS has advantages over using ICPMS alone, without any additional draw backs [17]. The addition of SEC does not change the general procedure of outcome of the ICPMS method [17]. It does however decrease the large dip in precision that is seen when a matrix with a substantial concentration is in solution with the lead being analyzed by ICPMS [17]. Experiments also reveal SEC-ICPMS’s ability to perform lead determinations in blood at much lower lead concentrations than ICPMS and some other analytical techniques [5,16-22].
Emission Spectrometry with a DC Aarc technique:
Spectrographically analyzing a sample of blood using a dc arc technique is a convenient, quick, and widely used analytical technique for the determination of lead in blood [18-19]. This technique is convenient and easy to use mainly because it requires significantly less sample preparation that other analytical techniques [18-19]. It is able to analyze whole blood, as long as the blood is not allowed to coagulate [18-19]. Prevention of coagulation is usually done by the addition of sodium heparin, EDTA, or potassium oxalate [18-19]. Trichloroacetic acid (TCA) solution is usually used to extract lead from uncoagolated blood, and in terms of this technique is used to prepare whole blood standards [18-19].
The quickness and ease of use that spectrographic analysis using a dc arc technique provides is offset by its disadvantages. One of these being that each spectrographic determination of lead in blood performed this way has to be done so within a certain range of lead in blood ppm [18]. Another disadvantage is that the instruments and procedures used for this method allow for high risk of contamination and loss of sample during its execution [17-20]. The final and most important disadvantage this method has is that while it does to some extent provide a good idea of lead exposure, it is not accurate enough to be used as an index of exposure for a particular region [18].
Note: In determination of lead in blood by atomic-absorption, -emission, and -fluorescence blood samples are typically prepared by dilution using Triton-X solutions and distilled water [4,20-22].
Atomic-Fluorescence Spectrometry:
It has been proven that this technique can be to analyze very small blood samples and to detect very low lead in blood concentrations [20]. The accuracy of atomic fluorescence spectrometry on average is greater than that of atomic-absorption techniques [20]. A fact that once lead to the widespread use of atomic-fluorescence spectrometry [20]. This is because before the development of a proper form of this technique, atomic-absorption techniques were the prevailing methods for determination of lead in blood [4,20-22]. Contamination of the blood samples used, prior to fluorescence, is the primary limiting factor for precision for this analytical technique [4,20-22]. Atomic-Fluorescence Spectrometry is accurate and precise enough to be used in determination of lead in blood, and for results of this method to be used in determining lead exposure and risk.
Atomic-Emission Spectrometry:
The atomic emission spectrometry technique is similar to atomic-fluorescence spectrometry [21]. The two techniques differ, however, in that atomic-emission spectrometry involves ashing during the execution of the method [20,21] . Ashing is a way of further preparing a blood sample for detection by an instrument [21]. For example, plasma ashing is process that involves depositing an aliquot of a blood sample on an electrode, heating a plasma gas, and allowing the gas to ash the blood sample for a certain period of time [21]. The lead can then be vaporized, atomized, excited and then detected [21].
Atomic-Absorption Spectrometry:
Atomic-Absorption Spectrometry is an analytical technique in which a temperature-controlled heating unit and a photodiode are used to measure, and by electric feedback, control the temperature of a carbon rod [4,22]. At the time that atomic absorption spectrometry was developed, there was a need for a proper method of determination of lead in blood [22]. It was developed before the worldwide reduction in lead emissions started in the 1970’s and become the prevalent method for blood lead determination after lead’s toxic effects on the human body become more known [4,22]. The preparation of blood samples for atomic absorption spectrometry is similar to the sample preparation in atomic emission spectrometry [4,20-22]. The two do differ, however, in that constant temperature monitoring is needed through ought the execution of the method’s procedure in order to get usable experimental results [4]. Atomic-absorption spectrometry is an effective method for the determination of lead in blood and can be used to establish exposure and risk. At the time when atomic-absorption spectrometry was developed it became the standard for blood lead determination, filling a hole, created by a lack of lead poisoning knowledge [4].
Flame and Flameless:
Atomic Fluorescence, -Emission, and – Absorption Spectrometry are similar techniques [4,19-22]. All three methods can involve the use of flame atomization [4,19-22]. The use of a flam during blood analyzing is an outdated practice. Flames, do however, allow for rapid analysis of blood samples [4,19-22]. A technique gets the moniker flame when atomization is done using a flame [4,19-22]. Flameless (heating during method done without flame) versions of these techniques are slower but more accurate and precise than their flame counterparts [4,19-22]. Although, increased reliability that is a property of flameless techniques, they also require greater attention paid to detail when executing procedures, particularly when it comes to regulating temperatures [4,19-22]. The regulation of temperatures during flameless techniques is crucial to their ability to accurately and precisely determine lead concentrations in blood [4,19-22].
Conclusion:
Lead and lead compounds have debilitating and sometimes fatal effects on human body [1-22]. Their ability to easily enter the human body is troubling to say the least. Despite the known toxic effects that exposure to lead has it has still managed to infiltrate almost every populated area of the world [1-15]. This presents the need for proper analytical methods to determine the concentration of lead in blood, which has proven to be a trustworthy indicator of lead emission and exposure in a certain area [1-22]. Although most methods developed so far are useful for determination of lead in blood, Inductively Coupled Plasma Mass Spectrometry with Size Exclusion Chromatography (ICPMS-SEC) is the preferred method [1-22]. ICPMS-SEC has proven to be more sensitive than other techniques [4,5,16-22]. A key feature of this technique is the use of lead in blood plasma as the indicator of blood lead levels instead of the more common lead in whole blood [1-22].
1. Haslam, R. H. (2003). "Lead poisoning." Paediatr Child Health 8 (2012). U.S. National Library of Medicine. 509-510. [web]
2. Needleman, H. (2004). "LEAD POISONING." Annual Review of Medicine 55: 209-222. [DOI]
3. Department of Health and Human Services (2011). "12th Report on Carcinogens (RoC)".[web]
4. Nise, G. and O. Vesterberg (1978). "Blood lead determination by flameless atomic absorption spectroscopy." Clinica Chimica Acta 84(1–2): 129-136. [DOI]
5. Rentschler, G., T. Lundh, et al. (2009). "Lead elimination from blood and plasma after lead poisoning." Toxicology Letters 189, Supplement(0): S227. [DOI]
6. United States Environmental Protection Agency. (2002) "Latest Findings on national Air Quality: 2002 Status and Trends." [web]
7. Gordon, J. N., A. Taylor, et al. (2002). "Lead poisoning: case studies." British Journal of Clinical Pharmacology 53(5): 451-458. [DOI]
8. (2010). Lead Poisoning. Black's Medical Dictionary, 42nd Edition. [web]
9. Ringold S, L. C. G. R. M. (2005). "Lead poisoning." JAMA: The Journal of the American Medical Association 293(18): 2304-2304. [DOI]
10.Couloures, K. and R. Vasan (2011). "Prenatal lead poisoning due to maternal exposure results in developmental delay." Pediatrics International 53(2): 242-244. [web]
11. (2009). lead poisoning. Mosby's Dictionary of Medicine, Nursing; Health Professions, Elsevier Health Sciences. [web]
12. (2005). lead poisoning. Collins Dictionary of Medicine, Collins.[web]
13. (2009). heme. Mosby's Dictionary of Medicine, Nursing; Health Professions, Elsevier Health Sciences. [web]
14. Jusko, T. A., C. R. Henderson, Jr., et al. (2008). "Blood Lead Concentrations < 10 μg/dL and Child Intelligence at 6 Years of Age." Environmental Health Perspectives 116(2): 243-248. [DOI]
15. Archer, N., C. Bradford, et al. (2012). "Relationship Between Prenatal Lead Exposure and Infant Blood Lead Levels." Maternal and Child Health Journal 16(7): 1518-1524. [DOI]
16. Takagi, M., J. Yoshinaga, et al. (2011). "Isotope Ratio Analysis of Lead in Blood and Environmental Samples by Multi-collector Inductively Coupled Plasma Mass Spectrometry." Analytical Sciences 27(1): 29-35. [DOI]
17. Gercken, B. and R. M. Barnes (1991). "Determination of lead and other trace element species in blood by size exclusion chromatography and inductively coupled plasma/mass spectrometry." Analytical Chemistry 63(3): 283-287. [DOI]
18. Rusak, D. A., R. L. Litteral, et al. (1997). "DC arc vaporization as a sample introduction technique for analysis of solids by ICP-OES." Talanta 44(11): 1987-1993. [DOI]
19. Steiner, R. L. and D. H. Anderson (1972). "Spectrographic Determination of Lead in Blood." Appl. Spectrosc. 26(1): 41-43. [web]
20. Omenetto, N., H. G. C. Human, et al. (1984). "Direct determination of lead in blood by laser-excited flame atomic-fluorescence spectrometry." Analyst 109(8): 1067-1070. [DOI]
21. Wensing, M. W., B. W. Smith, et al. (1994). "Capacitively coupled microwave plasma atomic emission spectrometer for the determination of lead in whole blood." Analytical Chemistry 66(4): 531-535. [DOI]
22. Selander, S. and K. Cramér (1968). "Determination of Lead in Blood by Atomic Absorption Spectrophotometry." British Journal of Industrial Medicine 25(3): 209-213. [web]
Determined to lead in Blood and Trial
By: Christopher Murray
Introduction:
Lead is an odorless, silver-bluish-white metal that is insoluble in water and has no known biological function in humans [1]. Exposure to lead and lead compounds can be harmful to humans, especially children [1-15]. Needleman notes that the poisonous properties of lead were first known to be described in the second century B.C. by the Greek physician, Nikander [2]. Nikander took note that after ingestion of lead by a person, colic and paralysis usually followed [2]. In spite of its poisonous properties, according to the U.S. Department of Health and Human Services, lead still managed to become the fifth most used metal in the world, behind iron, copper aluminum and zinc [3]. Due to its toxicity and prevalence in society, it is important that there is a proper determination of recent lead uptake in a particular area [1-5,7,9,14-22]. Determining the concentration of lead in blood is seen as a way of doing this [4,5,14-22]. Therefore, there is a need for reliable analytical techniques that can properly determine the concentration of lead in a blood.
Lead in our environment:
According to the a 2002 U.S. Environmental Protection Agency (EPA) report, Lead (Pb) is one of the six principle air pollutants (criteria pollutants) in our environment and one of four pollutants that are emitted directly from different sources [3,6]. Lead and lead compounds are commonly used in a variety of products, including piping, petrol additives, weights, professional paints, dyes, ceramics, ammunition, homeopathic remedies, cosmetics, cable coverings, sheet metal [1-3,6]. In the U.S. organic leads (mainly tetraethyl lead and tetramethyl lead) were once used as anti-knocking agents in motor vehicle fuels (primarily gasoline) [3]. As a result, automotive sources were the major contributor of lead emissions to the atmosphere, particularly in North America. In the early 1970’s the EPA initiated a phase-out of lead in gasoline [3,6]. Around this time, other countries also implemented programs aimed at decreasing the amount of lead emitted into the environment [1-3,6]. Since then, in the U.S., the use of lead in gasoline has fallen to 1% of its 1970 level and in 1996 the use of lead in fuel for on-road vehicles was completely banned [3,6]. By 2002 the overall emissions of lead had decreased about 93% [6]. As a result of similar regulations as in the U.S., between the years 1984-95, population blood lead concentration saw a “three-fold” decrease in the United Kingdom [7]. Today, lead’s largest use is in lead-acid storage batteries for motor vehicles and industrial use [3,6]. Also, the major sources of lead emissions to the atmosphere are now industrial processes, mainly the processing of metals [1-3,6].
Figure 1:
As a result of lead and lead compound’s use in industrial settings prior to 3 decades ago, adults were the main concern when lead exposure, particularly occupational exposure, was disused [1-3]. As the toxic affects lead has on humans were discovered regulations were put in place that decreased the number of adult lead poisoning cases reported each year [1-3,6-7]. The focus was then shifted from adults exposed to high does in industrial environments toward children, who may not present symptoms of lead poisoning until long after exposure [1-3,7,10,14]. Children are now at a greater risk of acute lead poisoning and plumbism (chronic lead poisoning) than adults [1-3,5,7,9,10,14,15]. In 1988 it was estimated that about 4 million children in North America had blood lead concentrations about 0.72 μmol/L (7.2x10-7 M), and thus were considered to be at risk of developing lead poisoning [7]. A lot of houses constructed before 1950 contain lead based paint [1]. Particularly in North America these houses may still be a health risk [1]. Today, Lead-based paint, lead dust, and lead in the soil are the leading causes of lead poisoning, particularly plumbism in children [1-3,7,9,14].
Lead entering the human body:
Lead can be released into the environments from both natural and anthropogenic sources [1-3,6,9]. The majority of our exposure and thus lead that are absorbed into the body results from anthropogenic sources [1-3,6,9]. When released, lead exists in both inorganic and organic forms, with inorganic being the more toxic to humans [3,7]. Despite its form, after emission into the environment lead is not degraded and is always available for human exposure [3,7].
Lead has a number of routes it can take to enter the human body [1-3,5-7,8,9,11,14] . It can be absorbed through the gastrointestinal tract (ingested), through the respiratory system (inhaled), or in rare occasions through dermal contact (contact with the skin) [1-3,5-7,8,9,11,14]. In adults, the respiratory tract is the main route of absorption, with anywhere from 30-70% of inhaled lead finding its way in the blood circulation [1-3,5-7,8,9,11,14]. This is because lead fumes are mainly found in industry [3,5,6]. Absorption that occurs through the gastrointestinal tract in adults is often incomplete, with only about 8-15% of ingested lead finding its way into blood circulation [1-3,5-7,8,9,11,14]. In children, the gastrointestinal tract is the primary sources of absorption, with about 50% of ingested lead ending up in blood circulation [1-3,5-7,8,9,10,11,14]. This is because of the fact that most children who develop lead poisoning, particularly in North America, do so from ingestion of lead paint chips [1-3,5-7,8,9,11,14]. When it comes to inhalation of lead and lead compounds the percent of lead that ends up in blood stream of children is comparable to that of adults, but children inhale a larger volume of air relative to their body sizes [7]. As a direct result of children’s large inhaled air to body size ratio, children absorb around three times more lead from the environment that adults [7]. In both adults and children, dermal absorption of lead and lead compounds is so rare and minute that the amount of lead that makes its way into the blood stream through dermal contact is negligible [2,3,7,11].
When lead or lead compounds are inhaled, particle size is the most important determinant of absorption [7]. Having an Iron deficiency and low calcium levels can increase absorption of lead by ingestion [2,7]. When in the body, lead tends to be stored in three major pools [2,7]. The greatest storage pool for lead is in dentine and the skeleton, which accounts for about 95% of lead decomposition in the body [2,7]. The next largest pool is comprised of the skin and muscle, which accounts for about 3% of lead deposition in the body [2,7]. The smallest and most important pool is the blood pool [2,7]. The blood pool of lead is “rapidly exchangeable” and despite its importance, accounts for only about 2% (95% is bound to erythrocyte membrane and 5% is in plasma) of the lead deposition in the body [2,7]. The lead in blood is the most important pool because the concentration of lead in blood can be used as an index of lead exposure [1-4,7,9,10,14,15]. Gordon describes blood lead as having a half-life of about 35 days, and bone lead as having a half-life of about 20-30 years [2,7].
Children, particularly infants, are at an even greater risk of lead poisoning due to their high rate of hand to mouth contact [10].
Lead’s effect on the human body:
General affects:
Lead poisoning is often asymptomatic, particularly acute poisoning and poisoning from lead with mild toxicity [1-3,5-7,8,9,11,14]. Some general symptoms of acute poisoning include: metallic taste, abdominal discomfort, lethargy, anorexia, headaches, and muscle weakness [1-3,5-7,8,9,11,12,14]. Some general symptoms of chronic lead poisoning (plumbism) include: vomiting, abdominal pain, coma, and a bluish lead line on the gums [1-3,5-7,8,9,11,12,14] .
Figure 2:
Biochemical and Blood affects:
Lead has a number of biochemical properties that account for its toxicity in humans [2,7]. Of these properties is that lead is a divalent cation that has the ability to bind strongly to sulfhydryl groups on proteins [2,7]. Lead, therefore, inhibits sulfhydryl dependent enzymes by distorting their structure [2,7]. The more important of the enzymes that lead inhibits include: 5-Aminolaevulinic acid dehydratase (ALAD), coproporphyrinogen oxidase, and ferrochelatase [2,7]. All of which are important in the synthesis of haem (heme[2,7,13]).
Figure 3:
Heme (haem) is an iron-containing non protein part of a hemoglobin molecule that allows for red blood cells to carry oxygen throughout the body [2,7,13]. Heme groups in hemoglobin molecules are comprised of a cyclic structure of four pyrrole compounds with an atom of iron at the center [2,7,13]. By interrupting the synthesis of heme in the body, lead increases the amount of unhealthy lead blood cells in circulation [2,7,13]. This effect of lead on the body is the reason that chronic exposure to lead can lead to development of anemia, which typically occurs when lead blood concentrations become greater than 2.4 μmol/L (2.4x10-6 M) [1,2,5-7,8,9,11,12,13,14]. Another biochemical property of the divalent lead cation is its ability to mimic calcium in the body [2,7]. This allows lead to compete for binding sites with calcium, which adversely affects endocrine and neuronal function [2,7]. Lead is picked up by mitochondria in cells distorting their shape, and inhibiting the proper execution of oxidative phosphorylation (cellular respiration) [1,2,7,8,9,11,12,14]. The last toxic biochemical property of lead is its ability to interact with nucleic acid binding proteins. This affects gene transcription of DNA, and as a result gene regulation [2,7].
Neurological and developmental affects:
Lead adversely affects the central nervous system (CNS) in adults, but does so to a greater extent in children [1,2,7-9,11,12,14]. Lead poisoning symptoms are primarily lethargy, fatigue and motor neuropathy, and encephalopathy (commonly seen in children with chronic lead exposure) [1-3,7-9,11,12,14]. Lead’s ability to mimic calcium allows it to interfere in certain neurotransmission pathways [2,7,10]. It causes sporadic neurotransmitter release and inhibits the needed stimulated releases [2,7,10]. Prenatal exposure to lead can stunt fetal development and have an adverse effect on the CNS and thus brain development of the resulting child [1-3,7-9,11,12,14,15]. Lead exposure is particularly dangerous for children younger than 6 years old [1-3,7-9,11,12,14]. Before this age, even the minutest exposure to lead can greatly damage the still developing central nervous system [2,3,7,9,10,15]. A study published in Environmental Health Perspectives illustrates that children under the age of 6 with blood lead concentrations as low as 5μg/dL have lower intelligence quotients (IQs) that they would have if they were not exposed to lead [2,7,9,10,14]. Over the age of six, lead exposure and, more specifically, blood lead concentrations in children have proven to be inversely proportional to full scale IQ and performance IQ scores[2,7,9,10,14].
Renal affects:
Lead neprophaty, interstitial nephritis, and renal failure are typically associated with chronic high levels of lead exposure and are seen mainly in industrial workers [1-3,7,8,9,11,12,14]. Acute lead poisoning typically presents itself as glycosuria, hyperphosphaturia, and aminoaciduria [1-3,7,8,9,11,12,14].
Diagnosing lead poisoning:
Diagnosis of acute lead poisoning and plumbism is difficult, mainly because most people exposed to lead are asymptomatic [1-3,7,8,9,11,12,14]. Also, the symptoms that do arise are common enough to be dismissed as individual conditions [1-3,7,8,9,11,12,14]. A physician’s discretion must be used, with the risk of a patient’s exposure to lead being a critical identifier for possible lead poisoning [1-3,7,8,9,11,12,14]. After risk is established, analytical techniques must be used to determine the exact concentration of lead in blood, which is the primary indicator of exposure [1-4,7,9,10,14-22]. Plasma lead levels have proven to be a greater indicator of exposure and risk than whole blood lead levels, when analyzing a sample of blood [5,16,17,20]. In some more modern techniques urine can be used to establish proof of exposure [1,2,3,7,22]. Techniques involving urine, however, can be unreliable and are primarily used in undeveloped nations [1]. In these nations lead concentrations are typically greater, thus requiring less sensitive analytical techniques [1,22].
Analyzing lead in the blood:
Inductively Coupled Plasma Mass Spectrometry:
Use:
Inductively coupled plasma mass spectrometry (ICP-MS) is a relatively modern technique used to analyze lead in blood plasma, rather than the lead in whole blood [4,5,16]. ICP-MS is widely used in the analysis of dried blood spots taken from newborns and infants to examine prenatal and neonatal lead exposure [10,15,16]. By taking the lead isotope ratio of environmental samples and comparing them with blood samples lead exposure levels for a particular area can be established [16]. Inductively coupled plasma (ICP) is known to be a superior ion source, allowing for efficient ionization, even in the mists of multiple ion sources, and for isotope ratio measurements with external standardization for an instrumental mass discrimination correction during ICP-MS [16].
Deduction:
When analyzed using ICP-MS the concentrations of matric elements prove to be inversely proportional to the precision of the determined lead isotope ratios [16]. This is one factor that contributes to a decreased signal intensity, which is a problem commonly experienced when performing ICP-MS [16]. This lowed signal intensity could also be attributed to ionization interference or space-charge effect [16].
ICP-MS is useful and accurate when determining isotope ratio measurements of lead in standard solution [16,17]. At concentrations greater than about 10mgkg-1, however, matrixes have proven to lower this accuracy in solution samples [16]. Despite this effect matrices have on the results of ICP-MS, it is still in general one of the more reliable analytical techniques that can be used when determining blood lead levels, and as a result, potential exposure or risk of exposure in a particular environment [4,7,15,16-22].
Inductively Coupled Plasma Mass Spectrometry + Size Exclusion Chromatography:
Combining size exclusion chromatography (SEC) to the previously described ICPMS has advantages over using ICPMS alone, without any additional draw backs [17]. The addition of SEC does not change the general procedure of outcome of the ICPMS method [17]. It does however decrease the large dip in precision that is seen when a matrix with a substantial concentration is in solution with the lead being analyzed by ICPMS [17]. Experiments also reveal SEC-ICPMS’s ability to perform lead determinations in blood at much lower lead concentrations than ICPMS and some other analytical techniques [5,16-22].
Emission Spectrometry with a DC Aarc technique:
Spectrographically analyzing a sample of blood using a dc arc technique is a convenient, quick, and widely used analytical technique for the determination of lead in blood [18-19]. This technique is convenient and easy to use mainly because it requires significantly less sample preparation that other analytical techniques [18-19]. It is able to analyze whole blood, as long as the blood is not allowed to coagulate [18-19]. Prevention of coagulation is usually done by the addition of sodium heparin, EDTA, or potassium oxalate [18-19]. Trichloroacetic acid (TCA) solution is usually used to extract lead from uncoagolated blood, and in terms of this technique is used to prepare whole blood standards [18-19].
The quickness and ease of use that spectrographic analysis using a dc arc technique provides is offset by its disadvantages. One of these being that each spectrographic determination of lead in blood performed this way has to be done so within a certain range of lead in blood ppm [18]. Another disadvantage is that the instruments and procedures used for this method allow for high risk of contamination and loss of sample during its execution [17-20]. The final and most important disadvantage this method has is that while it does to some extent provide a good idea of lead exposure, it is not accurate enough to be used as an index of exposure for a particular region [18].
Note: In determination of lead in blood by atomic-absorption, -emission, and -fluorescence blood samples are typically prepared by dilution using Triton-X solutions and distilled water [4,20-22].
Atomic-Fluorescence Spectrometry:
It has been proven that this technique can be to analyze very small blood samples and to detect very low lead in blood concentrations [20]. The accuracy of atomic fluorescence spectrometry on average is greater than that of atomic-absorption techniques [20]. A fact that once lead to the widespread use of atomic-fluorescence spectrometry [20]. This is because before the development of a proper form of this technique, atomic-absorption techniques were the prevailing methods for determination of lead in blood [4,20-22]. Contamination of the blood samples used, prior to fluorescence, is the primary limiting factor for precision for this analytical technique [4,20-22]. Atomic-Fluorescence Spectrometry is accurate and precise enough to be used in determination of lead in blood, and for results of this method to be used in determining lead exposure and risk.
Atomic-Emission Spectrometry:
The atomic emission spectrometry technique is similar to atomic-fluorescence spectrometry [21]. The two techniques differ, however, in that atomic-emission spectrometry involves ashing during the execution of the method [20,21] . Ashing is a way of further preparing a blood sample for detection by an instrument [21]. For example, plasma ashing is process that involves depositing an aliquot of a blood sample on an electrode, heating a plasma gas, and allowing the gas to ash the blood sample for a certain period of time [21]. The lead can then be vaporized, atomized, excited and then detected [21].
Atomic-Absorption Spectrometry:
Atomic-Absorption Spectrometry is an analytical technique in which a temperature-controlled heating unit and a photodiode are used to measure, and by electric feedback, control the temperature of a carbon rod [4,22]. At the time that atomic absorption spectrometry was developed, there was a need for a proper method of determination of lead in blood [22]. It was developed before the worldwide reduction in lead emissions started in the 1970’s and become the prevalent method for blood lead determination after lead’s toxic effects on the human body become more known [4,22]. The preparation of blood samples for atomic absorption spectrometry is similar to the sample preparation in atomic emission spectrometry [4,20-22]. The two do differ, however, in that constant temperature monitoring is needed through ought the execution of the method’s procedure in order to get usable experimental results [4]. Atomic-absorption spectrometry is an effective method for the determination of lead in blood and can be used to establish exposure and risk. At the time when atomic-absorption spectrometry was developed it became the standard for blood lead determination, filling a hole, created by a lack of lead poisoning knowledge [4].
Flame and Flameless:
Atomic Fluorescence, -Emission, and – Absorption Spectrometry are similar techniques [4,19-22]. All three methods can involve the use of flame atomization [4,19-22]. The use of a flam during blood analyzing is an outdated practice. Flames, do however, allow for rapid analysis of blood samples [4,19-22]. A technique gets the moniker flame when atomization is done using a flame [4,19-22]. Flameless (heating during method done without flame) versions of these techniques are slower but more accurate and precise than their flame counterparts [4,19-22]. Although, increased reliability that is a property of flameless techniques, they also require greater attention paid to detail when executing procedures, particularly when it comes to regulating temperatures [4,19-22]. The regulation of temperatures during flameless techniques is crucial to their ability to accurately and precisely determine lead concentrations in blood [4,19-22].
Conclusion:
Lead and lead compounds have debilitating and sometimes fatal effects on human body [1-22]. Their ability to easily enter the human body is troubling to say the least. Despite the known toxic effects that exposure to lead has it has still managed to infiltrate almost every populated area of the world [1-15]. This presents the need for proper analytical methods to determine the concentration of lead in blood, which has proven to be a trustworthy indicator of lead emission and exposure in a certain area [1-22]. Although most methods developed so far are useful for determination of lead in blood, Inductively Coupled Plasma Mass Spectrometry with Size Exclusion Chromatography (ICPMS-SEC) is the preferred method [1-22]. ICPMS-SEC has proven to be more sensitive than other techniques [4,5,16-22]. A key feature of this technique is the use of lead in blood plasma as the indicator of blood lead levels instead of the more common lead in whole blood [1-22].
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